Illinois Farmers Wrestle with Rootworm in First-Year Corn

Entomologists report that rotated corn is showing susceptibility to rootworm damage, even when planted to some Bt hybrids.

Just how bad is the rootworm resistance problem going to get in the central Corn Belt? No one can say with any degree of accuracy as a number of factors influence its severity across regions. But one thing is for certain: It’s getting worse in some parts of Illinois.

Earlier this week, University of Illinois Extension agronomist Mike Gray announced that "significant" western corn rootworm larval injury has been found in first-year corn fields in two Illinois counties, Livingston and Kankakee.

Gray, along with Joe Spencer an entomologist with the Illinois Natural History Survey, confirmed the problem in first-year cornfields planted to Bt rootworm hybrids (VT Triple PRO RIB – expresses the Cry3Bb1 protein).

"The fact that rotated corn is now showing susceptibility to rootworm damage, even when planted to certain Bt hybrids, is evidence that crop rotation in central and east central Illinois does not adequately confer a consistent level of root protection," Gray says.

Spencer collected adult rootworms from the infected fields, and bioassays will be done on the offspring to determine if the rotation resistant rootworm are also resistant to the Cry3Bb1 protein.

Gray writes that "If the bioassays confirm resistance to the Cry3Bb1 protein, producers across a wide swath of Illinois will have a formidable insect foe capable of overcoming both crop rotation and at least one Bt protein (Cry3Bb1)."